Week-11 Challenge: Braking

1. For a defined driving cycle, calculate the energy required for braking.

Sol: The drive Cycle considered is attached in the attachments & is as follows:

The time period of the drive cycle is from 0 to 60 seconds.

The MATLAB script is as follows and also has been attached in the attachments.

PLOT:

So for the given drive cycle, the total Braking energy required is 3.37 * 10^4 J or 0.0093 kWh.

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2. Why electric motor can’t develop braking torque at high speed similar to starting? How electric and mechanical brakes are coordinated?

Sol: From the graph, it is evident that till the motor reaches the critical speed (wbase in graph), the motor produces constant torque and once it crosses the critical speed, the motor goes into constant power region. The graph shows the acceleration characteristics.

For deceleration characteristics, the graph is mirrored to 4th Quadrant, i,e. The speed is +ve and Torque -ve.

For eg: If we consider an EV achieving 0 - 100 kmph in 10 seconds, the acceleration operation happens such that the power of the motor increase at constant torque till the motor reaches the critical speed & after the critical speed, the motor shifts to constant Power region and the torque begins to decrease.

For deceleration or braking condition, the speed v/s torque characteristics are shifted to 4th Quadrant where speed is +ve and Torque is -ve, hence we cannot expect the motor to produce same amount of torque as it did for acceleration. Thus for acceleration a motor has high Torque at low speeds and for deceleration it has low torque at high speeds.

Electric and mechanical brakes are coordinated using two strategies: Series and Parallel.

SERIES: Brakes will be applied one after another, so they are connected in series. This kind of strategy can be used wither for regenerative braking or mechanical braking i,e. both mechanical / regenerative braking cannot be deployed if series braking strategy is to be followed.

PARALLEL: In case of Parallel braking strategy both the brakes are applied simultaneously, i.e both at a time. Here both mechanical and regenerative braking can be deployed parallely.

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3. Make a MATLAB program which plots contour of given motor speed, torque and efficiency values. Attach the code as a .m file attach a screenshot of all the plots.

Sol: The MATLAB script is attached in the attachments and is as follows:

RESULT:

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